1. Field of the Invention
This invention relates to a lever type hoisting machine, and more particularly to a lever type hoisting machine having a simple structure capable of securely and easily pulling down the lower hook in no-load state.
2. Description of the Prior Art
In the conventional lever type hoisting machine, generally, a pressure bearing member was fixed on a drive shaft which was coupled to the load sheave by way of a transmission gear train, and friction members were disposed at both sides, and a reverse rotation preventive wheel rotatably only in one direction was inserted, and then a pressure drive wheel was screwed in to hold the reverse rotation preventive wheel with the pressure bearing member, and the pawl of operation lever was engaged with the pressure drive wheel. In such construction, by operating the operation lever to rotate the pressure drive wheel in the hoisting-up direction, the pressure drive wheel moves to the pressure bearing member side above the drive shaft to press the reverse rotation preventive wheel firmly against the pressure bearing member, so that the lower hook of the load chain wound on the load sheave is hoisted up.
Meanwhile, when pulling down the lower hook to a specified position in no-load state, that is, without any load in the lower hook of the hoisting machine, the pressure drive wheel is moved by the operation lever in a direction to depart from the friction member to keep the pressure drive wheel cleared from the cover or other part of the operation level, and the lower hook or the load chain coupled thereto is slowly moved downward.
In this construction, however, the following problems were experienced.
That is, while moving the lower hook downward, the pressure drive wheel may contact with the cover of the operation lever which covers its outside and side surfaces, and the rotation may be stopped momentarily. As a result, the pressure drive wheel moves toward the friction member side above the drive shaft to press against the friction member, which may cause to stop the rotation of the drive shaft. And the lower hook can no longer move downward. Hence, to lower the lower hook further downward, it is necessary to repeat the same operation from the beginning, which was very time-consuming and inconvenient.
To eliminate this inconvenience, it is necessary to hold the cover of operation lever tightly on the brake cover to cover the reverse rotation preventive wheel without any play, and for this purpose, the wall thickness of the fitting part of the both must be increased, and the operation lever must be kept at high precision so as not to incline toward the brake cover and must be also coupled in a reciprocable manner. In such a case, high precision machining was needed in the processing of the fitting parts, and it took time and labor, and the manufacturing cost was raised.